1. Field of the Invention
The present invention relates to a process for producing a particulate iron-antimony containing oxide composition having high compressive strength.
2. Background Art
Iron-antimony containing oxide compositions can be used as useful materials, such as inorganic ion-exchangers (see, for example, J. Inorg. Nucl. Chem. 4, 2121 (1981)), ceramics for sensors (see, for example, Proceedings of the 78th Annual Meeting of Catalyst Society of Japan (A), p. 141, (1996)) and, in addition, as precursors of catalysts and catalysts for fluidized beds.
Conventional methods for producing an iron-antimony containing oxide composition for use as a catalyst include, for example, one wherein a precipitate is obtained by coprecipitation from a solution of iron nitrate and antimony chloride in hydrochloric acid and then washed and calcined [see G. K. Boreskov et al.; Kinet. i Katal. 10 (6) 1350-1359 (1969), V. F. Anufrienko et al.; ibid. 14 (3) 716-721 (1973) and the like] and one which comprises oxidizing antimony trioxide with hydrogen peroxide to give antimony pentoxide, adding iron nitrate to a suspension of the resultant antimony pentoxide, heat-treating the mixture, drying the resultant material, and calcining the dried material (see U.S. Pat. No. 3,984,353). When use of an iron-antimony containing oxide composition as a catalyst for a fluidized bed reaction is contemplated, conventional production methods of such a catalyst include one which comprises: oxidizing metallic antimony with nitric acid; mixing the resultant antimony oxide with iron nitrate; neutralizing the mixture by addition of aqueous ammonia; washing the neutralized material with water; drying and calcining the washed material; pulverizing the calcined material; adding silica sol to the powder; and spray-drying and calcining the mixture (see U.S. Pat. No. 3,341,471) and one which comprises the steps of: adjusting an aqueous slurry containing a trivalent antimony compound, a ferric compound, nitrate ions, a polyvalent metal compound, and a silica sol as indispensable ingredients to a pH value of not more than 7; heat-treating the slurry at 40 to 150.degree. C. for at least 20 min while maintaining the slurried state; spray-drying the heat-treated slurry; and calcining the resultant particles (see U.S. Pat. No. 3,657,155).
When an iron-antimony containing oxide composition is to be used as a catalyst for a gaseous phase fluidized bed reaction, the catalyst should be excellent in catalytic activity, as well as in mechanical strength. For measuring the mechanical strength of the catalyst for fluidized bed operation, an attrition test by the ACC method has been generally performed in the art. In order to satisfy the above requirements for the catalyst, U.S. Pat. Nos. 3,341,471 and 3,657,155 noted above propose a process for producing an attrition-resistant catalyst for use in a fluidized bed wherein a silica component is used as one indispensable requirement. The catalyst, however, does not always have mechanical strength high enough to be applied to a fluidized bed reactor on a commercial scale, and particles of the catalyst are often crumbled and powdered in a cyclone section for collecting the catalyst generally provided in a fluidized bed reactor, resulting in large catalyst loss, which is a problem remaining unsolved in the art. Further, the strength of the materials produced by the process proposed by the above U.S. patents is unsatisfactory and frequently raises problems also for use of the material as a precursor of a catalyst and in other applications. It is known that compressive strength, defined as the minimum force necessary for crumbling a particle when a load is applied to the particle, is a preferred measure of the resistance to crumbling by mechanical shock. Thus, the development of an improved process for producing a particulate iron-antimony containing oxide composition having high compressive strength has been desired in the art and is an object of the present invention.